public class lanqiao_1874 {
    public static void main(String[] args) {
        System.out.println(sumNums(4));
    }
    static int sumNums(int n) {
        return back(n);
    }
    static int back(int n){
        if (n==0)
            return 0;
        return n+back(n-1);
    }
    
}
